The search for new quantum degrees of freedom has the potential for transformative impact on information processing technology. Currently, transistors or other switches in all electronic information processing devices rely on moving a puddle of electrons.
Valleys – extreme points in the energy band structure of periodic crystals – have been proposed as a new information carrier. In most materials, the valley degree of freedom does not couple to any external field. A unique situation in monolayer semiconductors has been discovered: light with opposite helicity may be used to control valley occupation.
We have discovered a new method to separate valley index using a designed metasurface. Excitons that carry different valley index are routed toward different directions in real space and momentum space, and photons emitted go to different directions according to their helicity.
